IL-21 peptides were first disclosed in WO 2000/53761, the polypeptide as encoded by the human IL-21 gene was shown in that application as SEQ ID No. 2. This pro-peptide is a 161 amino acid residue peptide. For convenience, the sequence is repeated in the present application as SEQ ID No. 1. It was initially believed that the mature peptide was the peptide consisting of amino acids residues 33 to 162 of SEQ ID No. 1; however more recently (WO 2004/112703) it has been suggested that the mature peptide is, in fact, amino acids residues 30 to 162 as shown in SEQ ID No. 2. IL-21 has been described as useful for the treatment of cancer, such as for instance malign melanoma. See for instance WO 2005/53761 and WO 2003/103589.
In spite of the efficacy shown by IL-21 in the treatment of various diseases, there remains a need for variants of IL-21 with improved or alternative properties, such as activity, selectivity, stability, and circulation time or biological half-life, to fulfil medical needs. Antagonism of the IL-21 receptor has also been described as having therapeutic use.
International Application WO2004/112703 describes a number of IL-21 variants.
International Application WO2006/111524 describes some IL-21 peptides which has improved binding to the IL-21 receptor.